1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling an uplink transmission and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (COMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
In one example, there may be three eNBs NB1-NB3, wherein the eNB NB1 may be a macrocell eNB with a larger coverage area, and the eNBs NB2-NB3 in the coverage area of the eNB NB1 may be microcell eNBs (or other small-cell eNBs) with smaller coverage areas. A UE may be in both the coverage areas of the eNBs NB1-NB2, e.g., communicate with the eNBs NB1-NB2 simultaneously, when the UE is configured with the dual connectivity. The UE may move from the coverage area of the eNB NB2 to the eNB NB3 due to movements of the UE, while the UE is still in the coverage area of the eNB NB1. In this situation, the UE does not know how to perform a UL transmission (e.g., control information, reference signal and/or data), because the UE is now in the coverage areas of the eNB NB1 and NB3. For example, the UE does not know whether it should transmit a sounding reference signal (SRS) for the eNB NB2. In another example, the UE may move out the coverage area of the eNB NB2 due to movements of the UE, while the UE is still in the coverage area of the eNB NB1. In this situation, the UE does not know how to perform a UL transmission (e.g., control information, reference signal and/or data), because the UE is only in the coverage area of the eNB NB1 now. For example, the UE does not know whether it should transmit a SRS for the eNB NB2. In the above examples, the UE may transmit data with a different allocation according to whether and how the SRS is transmitted. That is, the transmission of the data is affected by the transmission of the SRS which is unknown.
Thus, how to perform the UL transmission when a coverage area where the UE locates is changed is an important problem to be solved.